The aim of this study was to assess the effects of aerosol from two reference combustible cigarettes and two e-cigarettes by using the VC1 smoking machine with the air-liquid interface and to evaluate donor-to-donor variability of three EpiAirway tissue donors with the endpoints viability, barrier integrity, and gene promoter/expression regulation.

Abstract
The VITROCELL VC1 smoke exposure machine is an aerosol exposure system that has been used to conduct toxicological assessments with cigarettes and e-cigarettes and can be used with the human 3D EpiAirway tissue model (MatTek Corporation). The goals of this study were to assess exposure parameters of the VC1, and evaluate donor-to-donor variability of three EpiAirway tissue donors with the following endpoints: viability, barrier integrity, and gene promoter/expression regulation. Additionally, we applied the EpiAirway model to assess the effects of aerosol from two reference combustible cigarettes and two e-cigarettes. Whole smoke (WS) exposures with Kentucky Reference 3R4F cigarettes and Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) Monitor were conducted under International Organization for Standardization or Health Canada Intense (HCI) conditions, and e-cigarette exposures were conducted under modified HCI conditions. Particulate deposition and collection were consistent across independent assessments. A decrease in barrier function was accompanied with a dose-dependent decrease in viability for all donors. IC50 values were reproducible (coefficient of variations, CVs <20%) for all donors with both assays. Under HCI conditions, tissue viability and barrier integrity declined rapidly following 3R4F exposures, while no decline in either endpoint was observed with either e-cigarette. Increases in nuclear factor erythroid 2-related factor 2 (Nrf2) promoter activation through the antioxidant response element and gene expression associated with oxidative stress, inflammation, and metabolism were observed following 3R4F WS exposures, and the Nrf2 promoter was differentially regulated by 3R4F WS compared with gas–vapor-phase exposures. No activation in the Nrf2 promoter was observed for e-cigarette exposures. Collectively, the consistency of the VC1 system and EpiAirway model supports the use of these systems in respiratory toxicological assessments. Furthermore, these systems effectively discriminate the toxic impact of smoke from a combustible cigarette on cell viability and oxidative stress while showing no impact of e-cigarettes in these experiments.